The default for the expandable TOC is that it is a tab on the side of the viewer. With this feature, you can check a box to have the expandable TOC load immediately upon opening the digital flipbook.

Start at the main dashboard:

Go to Edition Tools:

Click on the Table of Contents tab within Edition Tools:

Click in the Open Upon Loading box:

Press Save before exiting to save your change.

Now, instead of a tab on the side, the TOC will open upon loading:

This feature gives you more customization options to enhance the look and feel of your content.